Embryonic development of neural connections between the cercus and terminal abdominal ganglion of Acheta domesticus are to be investigated by means of light and electron microscopy, with special attention to first contacts between center and periphery. Embryonic cerci will be ablated by laser beam, and the consequences for the development of the central nervous system will be examined in these animals. The behavior of grafted cercal regenerates on these cercusless animals will be observed, with the object of comparing quality of regeneration in the normal animal and one in which embryonic cerci were never present to send afferent fibers to the terminal ganglion. Homeotic mutants of Drosophila are being used to examine the pathways of sensory axons that develop out of their normal context. Projections to the central nervous system are mapped using cobalt chloride filling techniques.